/Engine/Plugins/Runtime/AR/Google/GoogleARCore/Source/GoogleARCoreBase/Public/GoogleARCoreTypes.h
Each point has a unique identifier (within a session) that is persistent across frames. That is, if a point from point cloud 1 has the same id as the point from point cloud 2, then it represents the same point in space.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintPure, Category="GoogleARCore|PointCloud") int GetPointId ( int Index )